This invention relates to power supplies for electronic equipment and, in particular, to inverters for generating high frequency sinusoidal AC voltages for electronics equipment used in telecommunications and computer systems. Typical examples of potential use are in personal computers, servers, routers, network processors, and opto-electronic equipment.
Segments of the personal computer (PC) industry have dramatically changed during the last decade. The future is even more challenging. A dramatic increase in the processor speeds of PCs has required an overwhelming increase in current and associated dynamics (very high slew rate). This already challenging technical requirement is further complicated by a need for voltage reduction, potentially to sub-volt levels.
In the past, there was virtually no challenge in powering computers. A multiple output, very slow power supply called a xe2x80x9cSilver Box (SB)xe2x80x9d was adapted to meet the requirements of every power demand. However, as silicon development progressed, multiple voltages of less than 3.3V were required. Voltage Regulator Modules (VRMs) on the processor Mother Board (MB) were a logical solution to that problem. Today, the number of VRMs required on the Mother Board is increasing. In addition to the VRMs, a large number of de-coupling capacitors are required in proximity of the processor to meet the requirements of very high slew rate of the current. This has resulted in a rapid increase in the cost, as well as a large reduction in overall efficiency, of the power delivery system.
A number of options for improving this situation have been explored. For example, Advanced Voltage Regulator Module (AVRM) offers the capability to supply high di/dt and high current, however, at increased cost, and with low efficiency and moderately high capacity of the de-coupling capacitors. Replacing low voltage DC distribution with higher DC voltage, such as 48V, is more promising but has a drawback of higher cost. Recently a novel High Frequency Alternating Current (HFAC) power delivery architecture has been proposed for powering the future generation PCs in reference entitled, xe2x80x9cPC Platform Power Distribution System: Past Application, Today""s Challenge and Future Directionxe2x80x9d published in the conference proceedings of International Telecommunications Energy Conference, Copenhagen, Denmark, June 1999 by J. Drobnik, L. Huang, P. Jain and R. Steigerwald. In the HFAC architecture, the system power supply (silver box) generates high frequency and high voltage. The HFAC is then fed to an individual AC-DC converter (ACVRM) and converted into DC of specific parameters at the point of use.
HFAC is conceptually the simplest architecture proposed to date, which deals with all of the power delivery issues defined above. This includes elimination of duplicated power conversions, and active energy steering without additional components.
The key to successful implementation of an HFAC power delivery system resides in the two stages of power conversion namely; DC to AC high frequency conversion stage and the stage that converts high frequency AC to DC.
FIG. 1 shows a block diagram of a conventional DC to high frequency AC inverter 100. The inverter 100 includes a full-bridge inverter 104 having an input 104A for receiving a DC input voltage 102 and providing an output 104B. The output 104B is connected at 106 to an input 108A of a resonant circuit 108. An output 108B of the resonant circuit 108 provides a high frequency AC output voltage 110. The AC output voltage 110 is fed back 112 to an input 114A of a phase-shift modulation circuit 114. The modulation circuit provides four outputs 114B connected at 116 to four inputs 118A of a gate drive circuit 118. The gate drive circuit 118 has four outputs 118B connected at 120 to four inputs 104C of the inverter 104.
A number of power circuit configurations to implement the full-bridge inverter and resonant circuit of FIG. 1 are possible but the circuits as shown in FIGS. 2A and B are the circuits most commonly used in these implementations.
FIG. 2A shows the full-bridge inverter 104 and the resonant circuit 108 sections of a conventional inverter 200 which was described in xe2x80x98A 20 kHz Hybrid Resonant Power Source for the Space Stationxe2x80x99, IEEE Trans. on Aerospace and Electronics Systems, vol. 25, No. Jul. 4, 1989, 491-496 by P. Jain and M. Tanju. The full-bridge inverter 104 includes a first switch 202, a second switch 204, a third switch 206, and a fourth switch 208. Each switch 202,204,206,208 is preferably an N-channel field-effect transistor (FET). The resonant circuit 108 includes a series resonant circuit 210, a parallel resonant circuit 212, and a transformer 214.
The full-bridge inverter 104 produces a quasi-square voltage at its output 106, which is controlled using a phase-shift modulation circuit 114 (FIG. 1) commonly used in such applications. Both the series 210 and parallel 212 resonant circuits are tuned to an operating frequency of the inverter. Although the resonant circuit 108 produces a regulated sinusoidal voltage at its output 110, this inverter 200 does not provide zero-voltage switching conditions for at least two of the four switches 202,204,206,208, which results in higher switching losses at higher operating frequencies. Therefore, the operation of this circuit is limited to lower operating frequencies.
FIG. 2B shows the full-bridge inverter 104 and the resonant circuit 108 sections of a conventional inverter 250 which was described in xe2x80x98Constant frequency resonant DC/DC converterxe2x80x99, U.S. Pat. No. 5,157,593, Oct. 20, 1992 by P. Jain. The full-bridge inverter 104 is identical to the one shown in FIG. 2A. The resonant circuit 108 includes a series resonant circuit 210, a parallel resonant circuit 252, and a transformer 214.
The full-bridge circuit 104 produces a quasi-square voltage at its output 106, which is controlled using a phase-shift modulation circuit 114 (FIG. 1) commonly used in such applications. In this configuration, the series resonant circuit 210 is tuned to an operating frequency of the inverter 250 while the parallel circuit 252 is tuned at a frequency, which is lower than the operating frequency. Although the resonant circuit 108 produces a regulated sinusoidal voltage at its output 110 and provides zerovoltage switching conditions for all the four switches 202,204,206,208, the de-tuning of the parallel branch 252 requires the series resonant components 210 and the output transformer 214 to have higher maximum ratings and hence be more expensive.
Another fundamental problem that limits the operation of the inverter circuits of FIGS. 2A and B at higher operating frequencies is gate circuit losses of the FETs 202,204,206,208 used in the full-bridge circuit 104. FIG. 3 shows a graph 300 of typical gating signals A1302, A2304, B1306, and B2308 produced by the phase-shift circuit 114. FIG. 4 shows a graph 400 of gate voltage (VgA1) 402, gate current (igA1) 404, instantaneous gate power (pgA1) 406, and average gate power (PgA1) 408 for a gate 202A of the first FET switch 202. This graph 400 clearly shows that when a rectangular voltage pulse 402 is applied to the gate 202A of the FET 202, which has a capacitance, a pulsating current 404 is drawn from this voltage. This causes the power loss 406 in the gate circuit, which is approximately given by Cg*Vg2*f 408 (where Cg is gate capacitance; Vg is gate voltage; and, f is the operating frequency). At higher frequency, the gate losses are prohibitively high, which limits the operation of inverter circuits of FIGS. 2A and B at very high frequency.
It is clear from the above discussion that the conventional approaches to converting DC to high frequency AC have low conversion efficiency due to high switching losses.
There therefore exists a need for an inverter topology, which is capable of operating at substantially higher frequencies and has no, or very small, switching losses, including gate circuit losses.
It is therefore an object of the invention to provide a DC/AC inverter, which forms a high frequency sinusoidal AC source.
The invention therefore provides a high-frequency resonant sine wave DC to AC inverter suitable for use in a personal computer (PC) power supply, which includes a full-bridge inverter, a resonant circuit, a phase shift modulation circuit, and a resonant gate driver. The resonant gate driver provides sinusoidal gate drive signals to the full-bridge inverter enabling highly efficient operation on the inverter.
The invention further provides a method of driving an inverter to convert direct current (DC) to alternating current (AC), comprising a step of receiving square wave gating signals at a resonant gate driver and modifying the square wave gating signals to form sinusoidal gating signals for driving the inverter.